Methods for the synthesis of chiral kynurenine compounds

ABSTRACT

Provided are methods for synthesizing compounds, including chiral kynurenine compounds. The methods are suitable for large-scale manufacture and produce the chiral kynurenines compounds in high chemical purity and high chiral purity.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/785,807, filed Mar. 14, 2013, the disclosure of which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present inventions relate to methods for synthesizing compounds,including chiral kynurenine compounds and related compounds.

BACKGROUND

Kynurenic acid is a metabolically related brain constituent withanticonvulsant and neuroprotective properties (Stone, T. W.; Pharmacol.Rev. 1993, 45, 309-379). The biological activities of variousderivatives of the kynurenic acid and their kynurenine precursors havebeen studied (Camacho, E. et al. J. Med. Chem. 2002, 45, 263-274;Varasi, M. et al. Eur. J. Med. Chem. 1996, 31, 11-21; Salituro, F. G. etal. J. Med. Chem. 1994, 37, 334-336). Kynurenine compounds are convertedto kynurenic acids in vivo.

An enantioselective synthesis described by Salituro et al. was used forthe synthesis of gram quantities of L-4-chlorokynurenine (Salituro, F.G. et al. J. Med. Chem. 1994, 37, 334-336). This synthesis was notpractical for scale up on a larger manufacturing scale due to the use ofreagents such as trimethyl tin chloride, sodium hydride andtert-buthyllithium and the lack of availability of certain buildingblocks.

A racemic synthesis of 4-chlorokynurenine was reported in Varasai et al.Eur. J. Med. Chem. 1996, 31, 11-21. However, experiments for theseparation of the enantiomers by crystallization of diasteromeric saltswere not successful, nor was preparative HPLC substantially successful,due to low solubility.

There is a need for a convenient synthesis for chiral kynurenines andrelated compounds using commercially available reagents that does notrequire the use of toxic or highly reactive reagents or extensivepurification techniques. There is a need for syntheses suitable forlarge-scale manufacture and that can produce chiral kynurenines andrelated compounds in high chemical purity and high chiral purity.

All publications, patents, and patent applications cited herein arehereby incorporated by reference in their entirety for all purposes.

SUMMARY

Provided are methods for the synthesis of compounds including chiralkynurenine compounds and related compounds. In a specific embodiment,methods are provided for the synthesis of L-4-chlorokynurenine. Incertain embodiments, the syntheses advantageously use commerciallyavailable reagents and avoid the use of toxic or highly reactivereagents or extensive purification techniques. In certain embodiments,syntheses are provided that are suitable for large-scale manufacture andthat can produce compounds including the chiral kynurenines compoundsand related compounds in high chemical purity and high chiral purity.

In one embodiment, the present disclosure provides a method of preparinga compound of Formula I or a pharmaceutically acceptable salt,polymorph, hydrate, solvate, tautomer, or stereoisomer thereof:

wherein each R is independently selected from the group consisting ofhydrogen, halogen, alkyl, and substituted alkyl; and

wherein n=0-4;

the method comprising:

a) acylating an aniline compound of Formula II with chloroacetonitrilein the presence of aluminum trihalide and boron trihalide to afford anacylated aniline compound of Formula III:

b) alkylating the acylated aniline compound of Formula III withacetamido diethyl malonate to afford a diethyl ester compound of FormulaIV:

c) decarboxylating the diethyl ester compound of Formula IV to afford anacylated kynurenine compound of Formula V:

and

d) resolving the acylated kynurenine compound of Formula V with anenzyme to afford the compound of Formula I:

In some embodiments, the enzyme is acylase I from Aspergillus melleus.In other embodiments, at least 10 g of the compound of Formula I isproduced. In other embodiments, at least 100 g of the compound ofFormula I is produced. In other embodiments, at least 500 g of thecompound of Formula I is produced. In other embodiments, the acylatingstep a) comprises adding the chloroacetonitrile to a toluene solution ofthe aniline compound II, the boron trihalide, and the aluminum trihalideat a first temperature of 0 to 10° C. followed by heating to a secondtemperature of 55 to 60° C. In other embodiments, the alkylating step b)is carried out in the presence of an alkali metal salt. In otherembodiments, the alkali metal salt is sodium iodide.

In another embodiment, the present disclosure provides a method ofpreparing a compound of Formula Ia:

the method comprising:

a) acylating 3-chloroaniline (IIa) with chloroacetonitrile in thepresence of aluminum trihalide and boron trihalide to afford1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (IIIa):

b) alkylating 1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (IIIa) withacetamido diethyl malonate to afford2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa):

c) decarboxylating2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa) to afford2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyric acid (Va):

and

d) resolving 2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyricacid (Va) with an enzyme to the compound of Formula Ia:

In some embodiments, the enzyme is acylase I from Aspergillus melleus.In other embodiments, at least 10 g of the compound of Formula Ia isproduced. In other embodiments, at least 100 g of the compound ofFormula Ia is produced. In other embodiments, at least 500 g of thecompound of Formula Ia is produced. In other embodiments, the acylatingstep comprises adding the chloroacetonitrile to a toluene solution ofthe 3-chloroaniline, the boron trihalide, and the aluminum trihalide ata first temperature of 0 to 10° C. followed by heating to a secondtemperature of 55 to 60° C. In other embodiments, the alkylating step iscarried out in the presence of an alkali metal salt. In otherembodiments, the alkali metal salt is sodium iodide.

DETAILED DESCRIPTION

Provided are methods of preparing compounds, including chiral kynureninecompounds and related compounds.

DEFINITIONS

The term “alkyl” includes saturated aliphatic groups includingstraight-chain, branched-chain, cyclic groups, and combinations thereof.Examples of alkyl groups include, but are not limited to, groups such asmethyl, ethyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, sec-butyl,t-butyl, pentyl, n-pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl,dodecyl, neopentyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,and adamantyl. Cycloalkyl groups can consist of one ring, including, butnot limited to, groups such as cycloheptyl, or multiple fused rings,including, but not limited to, groups such as adamantyl or norbornyl.

“Substituted alkyl” includes alkyl groups substituted with one or moresubstituents including, but not limited to, groups such as halogen(fluoro, chloro, bromo, and iodo), alkoxy, acyloxy, amino, hydroxyl,mercapto, carboxy, benzyloxy, phenyl, benzyl, cyano, nitro, thioalkoxy,carboxaldehyde, carboalkoxy and carboxamide, or a functionality that canbe suitably blocked, if necessary for purposes of the invention, with aprotecting group. Examples of substituted alkyl groups include, but arenot limited to, —CF₃, —CF₂CF₃, and other perfluoro and perhalo groups;—CH₂—OH; —CH₂CH₂CH(NH₂)CH₃, etc.

The term “halogen,” “halide,” or “halo” as used herein includes theGroup VIIa elements (Group 17 elements in the 1990 International Unionof Pure and Applied Chemistry (IUPAC) Periodic Table, IUPAC Nomenclatureof Inorganic Chemistry, Recommendations 1990) and includes fluoro,chloro, bromo, and iodo substituents.

Compounds

A variety of compounds, including chiral kynurenine compounds andrelated compounds, may be synthesized using the methods disclosedherein. In some embodiments, a compound of Formula I may be synthesized,or a pharmaceutically acceptable salt, polymorph, hydrate, solvate,tautomer, or stereoisomer thereof:

wherein each R is independently selected from the group consisting ofhydrogen, halogen, alkyl, and substituted alkyl; and

wherein n=0 to 4.

Where a chiral center is shown, any stereoisomer is within the scope ofthe invention. Where an (S) isomer is disclosed, the corresponding (R)isomer is within the scope of the invention. Where an (L) isomer isdisclosed, the corresponding (D) isomer is within the scope of theinvention. Where an (R) isomer is disclosed, the corresponding (S)isomer is within the scope of the invention. Where a (D) isomer isdisclosed, the corresponding (L) isomer is with in the scope of theinvention.

In a particular embodiment the compound is L-4-chlorokynurenine (Ia),which also is referred to by the chemical name(S)-2-amino-4-(2-amino-4-chlorophenyl)-4-oxobutanoic acid:

Where a compound is described herein, all stereoisomers thereof are alsocontemplated, including diastereomers and enantiomers, as well asmixtures of stereoisomers, including, but not limited to, racemicmixtures.

Some compounds of the present invention may exhibit polymorphism. Thescope of the present invention includes all polymorphic forms of thecompounds according to the invention.

Methods of Preparation

Methods of preparing a compound, for example of Formula I, or apharmaceutically acceptable salt, polymorph, hydrate, solvate, tautomer,or stereoisomer thereof are provided:

wherein each R is independently selected from the group consisting ofhydrogen, halogen, alkyl, and substituted alkyl; and

wherein n=0 to 4.

Also provided is a method of preparing a compound, for example ofFormula I, or a pharmaceutically acceptable salt, polymorph, hydrate,solvate, tautomer, or stereoisomer thereof:

wherein each R is independently selected from the group consisting ofhydrogen, halogen, alkyl, and substituted alkyl; and

wherein n=0-4;

the method comprising:

a) acylating an aniline compound of Formula II with chloroacetonitrilein the presence of aluminum trihalide and boron trihalide to afford anacylated aniline compound of Formula III:

b) alkylating the acylated aniline compound of Formula III withacetamido diethyl malonate to afford a diethyl ester compound of FormulaIV:

c) decarboxylating the diethyl ester compound of Formula IV to afford anacylated kynurenine compound of Formula V:

and

d) resolving the acylated kynurenine compound of Formula V with anenzyme to afford the compound of Formula I:

The R enantiomers of the compounds of Formulas I are also contemplated.

In one exemplary embodiment, the enzyme is acylase I from Aspergillusmelleus. However, other acylase enzymes having similar functional,enzymatic activity would be known to persons skilled in the art.

In another embodiment, at least 10 g of the compound of Formula I isproduced using the disclosed methods. In another embodiment, at least100 g of the compound of Formula I is produced using the disclosedmethods. In a particular embodiment, at least 500 g of the compound ofFormula I is produced using the disclosed methods. Alternatively oradditionally, the overall yield is at least 50% or more.

In another embodiment, the acylating step is carried out by addingchloroacetonitrile to a solution of aniline (II), boron trihalide, andaluminum trihalide in toluene at a temperature of about 0 to 10° C.followed by heating the reaction mixture to a temperature of about 55 to60° C.

In another embodiment, the alkylating step is carried out in thepresence of an alkali metal salt. Examples of such salts are thechloride, bromide, and iodide salts of sodium or potassium. In apreferred embodiment, the alkali metal salt is sodium iodide.

In another embodiment, provided is a method of preparing a compound ofFormula Ia or a pharmaceutically acceptable salt, polymorph, hydrate,solvate, tautomer, or stereoisomer thereof:

the method comprising:

a) acylating 3-chloroaniline (IIa) with chloroacetonitrile in thepresence of aluminum trihalide and boron trihalide to afford1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (IIIa):

b) alkylating 1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (IIIa) withacetamido diethyl malonate to afford2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa):

c) decarboxylating2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa) to afford2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyric acid (Va):

and

d) resolving 2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyricacid (Va) with an enzyme to afford the compound of Formula Ia:

The R enantiomers of the compounds of Formulas Ia are also contemplated.

In one exemplary embodiment, the enzyme is acylase I from Aspergillusmelleus. However, other acylase enzymes having similar functional,enzymatic activity would be known to persons skilled in the art.

In another embodiment, at least 10 g of the compound of Formula Ia isproduced using the disclosed methods. In another embodiment, at least100 g of the compound of Formula Ia is produced using the disclosedmethods. In a particular embodiment, at least 500 g of the compound ofFormula Ia is produced using the disclosed methods. Alternatively oradditionally, the overall yield is at least 50% or more.

In another embodiment, the acylating step is carried out by addingchloroacetonitrile to a solution of aniline (IIa), boron trihalide, andaluminum trihalide in toluene at a temperature of about 0 to 10° C.followed by heating the reaction mixture to a temperature of about 55 to60° C.

In another embodiment, the alkylating step is carried out in thepresence of an alkali metal salt. Examples of such salts are thechloride, bromide, and iodide salts of sodium or potassium. In apreferred embodiment, the alkali metal salt is sodium iodide.

In certain embodiments, the methods allow for the production ofcompositions comprising compound of Formulas I or Ia in high purity, orin high enantiomeric excess. In some embodiments, a the compositioncomprising the compound of Formulas I or Ia is provided in a range ofabout 95% to about 100% for both chemical purity and enantiomericexcess. In some embodiments, a the composition comprising the compoundof Formulas I or Ia is provided with about 70%, 75%, 80%, 81%, 82%, 83%,84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%,98%, 99%, or 100% purity. In other embodiments, compositions comprisingthe compound of Formulas I or Ia have a high enantiomeric purity of adesired enantiomer in about 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%,87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, and100% enantiomeric excess (ee).

The invention will be further understood by the following non-limitingexamples.

Materials and Methods

Reagents and solvents were used as received from commercial suppliers.HPLC analyses were performed using a TSP-SpectraSYSTEM HPLC in a WaterSymmetry Shield RP18, 75×4.6 mm. Solvents, water/acetonitrile/0.1% TFAin water-acetonitrile (9:1); gradient, 80:10:10 to 0:90:10 in 12 minthen 80:10:10; flow rate, 1 ml/min; wavelength, 230 nm. Enantiomericexcess was determined by TSP-SpectraSYSTEM HPLC on a Chirobiotic T,250×4.6 mm. Solvents, water/ethanol 1:1; flow rate, 1 ml/min;wavelength, 230 nm; t_(R) 6.13 for L-isomer and 15.60 min for D-isomer.HPLC analyses are reported in area %.

Example 1 Preparation of 1-(2-Amino-4-chloro-phenyl)-2-chloro-ethanone(IIIa)

At a jacket temperature of 0° C., 1 M BCl₃ in dichloromethane (45 L, 45mol, 1.1 equiv) was transferred into the reactor and toluene (13 L) wasadded. At −5 to 3° C. a solution of 3-chloroaniline (IIa, 4.5 L, 42 mol)in toluene (39 L) was added over 38 min followed after 31 min byaluminum trichloride (5.8 kg, 43 mol, 1.0 equiv). After 3 min, asolution of chloroacetonitrile (3.4 L, 54 mol, 1.3 equiv) in toluene(3.4 L) was added at −4 to 6° C. during 10 min. Heating to 65° C. at amaximal jacket temperature of 100° C. took 47 min, the mixture wasstirred at 65° C. overnight. The reaction mixture was added to 1Naqueous HCl (81 L) over 41 min at 43° C. and stirred for 30 min at 48°C. After cooling to 20° C., the phases were separated and the aqueousphase was extracted twice with dichloromethane (2×40 L). The combinedorganic phases were washed with water (20.5 L). Dichloromethane (75 L)was removed by distillation under reduced pressure (jacket temperature45° C.) and heptane (55 L) was added to the solution at 40° C. Coolingto 5° C., filtration, and washing with heptane (15 L) led to isolationof 1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (Ma, 2.5 kg, 12 mol,29% yield, 99.2% a/a HPLC).

Example 2 Preparation of2-Acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa)

To a solution of acetamido diethyl malonate (5.87 kg, 27.0 mol, 1.01equiv) in ethanol (31.5 L) was added 21% sodium ethoxide in ethanol(12.1 L, 32.4 mol, 1.21 equiv) at 22° C. A mixture of1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (Ma, 5.44 kg, 26.7 mol),sodium iodide (0.60 kg, 4.0 mol, 0.15 equiv), ethanol (17 L), andtetrahydrofuran (THF, 17 L) was dosed into the reactor at 40° C. andstirring was continued for 2 h at 45° C. Water (36 L) was added afterevaporation of the reaction mixture to 45% of the original volume andthe aqueous phase was extracted twice with dichloromethane (34.5 L, 20L). The combined organic phases were washed with water (14 L). Afterremoval of 25% of the original volume by distillation under reducedpressure, isopropanol (32 L) was added and 50% thereof distilled off. At60° C., heptane (11 L) was added. Cooling the mixture to 5° C.,filtration and washing with isopropanol/heptane 1:1 (15 L) afforded2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa, 5.86 kg, 15.2 mol, 57% yield, 99.5% a/a HPLC).

Example 3 Preparation of2-Acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyric acid (Va)

A solution of2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa, 5.80 kg, 15.1 mol) in water (3.8 L), dioxane (55 L)and 30% NaOH (7.7 L, 76.8 mol, 5.09 equiv) was heated to reflux at ajacket temperature of 110° C. for 45 min. Acetic acid (12.0 L) was addedat 65-70° C. and the suspension was heated to reflux while maintaining ajacket temperature of 110° C. for 1.5 h. Saturated aqueous NaCl (30 L)and ethyl acetate (54 L) were added at 20° C., the phases separated, andthe aqueous phase was extracted with ethyl acetate/dioxane 1:1 (40 L).The combined organic phases were then washed with a saturated aqueoussolution of NaCl (14.5 L). The organic phase was evaporated to dryness(the product crystallized prior to complete evaporation) and strippedwith ethanol (15.5 L) to afford2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyric acid (Va, 3.65kg, 12.8 mol, 85% yield, 92.7% a/a HPLC).

Example 4 Preparation of L-4-Chlorokynurenine (Ia)

A solution of 2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyricacid (Va, 3.57 kg, 12.6 mol) in water (52 L) and 0.1 M cobalt(II)chloride solution (108 mL, 0.01 mol) was heated to 35° C. Addition of 5M LiOH in water (2.55 L, 12.8 mol, 1.02 equiv) gave a solution (pH=8.5)to which Acylase I (0.79 kg) in water (3.0 L) was added (pH=7.3). The pHwas adjusted to 8.6 by addition of 5 M LiOH in water (0.21 L) andstirred for 19 h. Ethyl acetate/THF 1:1 (15.5 L) was added at 20° C. andthe mixture acidified with 32% aqueous HCl (2.1 L). The layers wereseparated and the aqueous phase was filtered via a Zetacarbon and inlinefilter. The organic phase was extracted twice with 0.1 N HCl (2×11 L).The filtrate was extracted twice with ethyl acetate/THF (2×13.5 L). Theaqueous layer was also filtered via a Zetacarbon and inline filter.Butanol (8.0 L) was added and the volume reduced to 7 L by azeotropicdistillation at reduced pressure. The pH was adjusted to 6.2 by additionof 5 M LiOH (3.7 L) and 32% aqueous HCl (0.5 L). Cooling to 5° C.,filtration and washing with water (2×1.5 L) provided crudeL-4-chlorokynurenine (Ia). Dissolution of L-4-chlorokynurenine (Ia) inwater (4.0 L) and 5 M LiOH (1.4 L) at pH=11 to 12, filtration of theresidue, washing with 0.1 M LiOH (2×0.33 L) and readjusting the pH to6.2 by addition of 32% aqueous HCl (0.8 L) led to a suspension.Filtration and washing the filter cake with water (2×1.0 L) and ethanol(1.0 L) afforded L-4-chlorokynurenine (Ia, 605 g, 2.49 mol, 19.8% yield,98.8% a/a HPLC).

We claim:
 1. A method of preparing a compound of Formula I or apharmaceutically acceptable salt, polymorph, hydrate, solvate, tautomer,or stereoisomer thereof:

wherein each R is independently selected from the group consisting ofhydrogen, halogen, alkyl, and substituted alkyl; and wherein n=0-4; themethod comprising: a) acylating an aniline compound of Formula II withchloroacetonitrile in the presence of aluminum trihalide and borontrihalide to afford an acylated aniline compound of Formula III:

b) alkylating the acylated aniline compound of Formula III withacetamido diethyl malonate to afford a diethyl ester compound of FormulaIV:

c) decarboxylating the diethyl ester compound of Formula IV to afford anacylated kynurenine compound of Formula V:

and d) resolving the acylated kynurenine compound of Formula V with anenzyme to afford the compound of Formula I:


2. The method of claim 1, wherein the enzyme is acylase I fromAspergillus melleus.
 3. The method of claim 1, wherein at least 10 g ofthe compound of Formula I is produced.
 4. The method of claim 3, whereinat least 100 g of the compound of Formula I is produced.
 5. The methodof claim 4, wherein at least 500 g of the compound of Formula I isproduced.
 6. The method of claim 1, wherein the acylating step a)comprises adding the chloroacetonitrile to a toluene solution of theaniline compound II, the boron trihalide, and the aluminum trihalide ata first temperature of 0 to 10° C. followed by heating to a secondtemperature of 55 to 60° C.
 7. The method of claim 1, wherein thealkylating step b) is carried out in the presence of an alkali metalsalt.
 8. The method of claim 7, wherein the alkali metal salt is sodiumiodide.
 9. A method of preparing a compound of Formula Ia or apharmaceutically acceptable salt, polymorph, hydrate, solvate, tautomer,or stereoisomer thereof:

the method comprising: a) acylating 3-chloroaniline (IIa) withchloroacetonitrile in the presence of aluminum trihalide and borontrihalide to afford 1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone(IIIa):

b) alkylating 1-(2-amino-4-chloro-phenyl)-2-chloro-ethanone (IIIa) withacetamido diethyl malonate to afford2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa):

c) decarboxylating2-acetylamino-2-[2-(2-amino-4-chloro-phenyl)-2-oxo-ethyl]-malonic aciddiethyl ester (IVa) to afford2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyric acid (Va):

and d) resolving 2-acetylamino-4-(2-amino-4-chloro-phenyl)-4-oxo-butyricacid (Va) with an enzyme to the compound of Formula Ia:


10. The method of claim 9, wherein the enzyme is acylase I fromAspergillus melleus.
 11. The method of claim 9, wherein at least 10 g ofthe compound of Formula Ia is produced.
 12. The method of claim 11,wherein at least 100 g of the compound of Formula Ia is produced. 13.The method of claim 12, wherein at least 500 g of the compound ofFormula Ia is produced.
 14. The method of claim 9, wherein the acylatingstep comprises adding the chloroacetonitrile to a toluene solution ofthe 3-chloroaniline, the boron trihalide, and the aluminum trihalide ata first temperature of 0 to 10° C. followed by heating to a secondtemperature of 55 to 60° C.
 15. The method of claim 9, the alkylatingstep is carried out in the presence of an alkali metal salt.
 16. Themethod of claim 15, wherein the alkali metal salt is sodium iodide.